1. Field of the Invention
The present invention relates to a micro fan, and more particularly, the present invention relates to a micro fan in which each blade has an airfoil-shaped cross-section and is applied with a helical twist by twisting at a predetermined angle a span between a root and a tip of the blade, to generate optimum volume flow rate and wind pressure when the blade is rotated, thereby improving rotational efficiency and reducing electric power consumption and rotation noise.
2. Description of the Related Art
Generally, a micro fan is mainly used in a limited space such as in a notebook computer or a personal computer, for cooling and dissipating driving heat existing in a driving device such as a micro-processor or a VGA card, which generates heat upon driving. In these days, it is the norm to use a single rotation type axial flow fan having a small size as a micro fan.
A micro fan is directly locked to a micro-processor or is independently attached to an inside structure in a notebook computer or the like. At this times due to the fact that capacity and speed of a CPU for respective driving devices are multiplied while a personal computer trends toward miniaturization of its components, because load capacity is rapidly raised, heat of a high temperature is generated.
This driving heat generated in the CPU can cause driving failure due to overheating when it is not properly cooled and can induce damage to main components of the computer, thereby resulting in a breakdown of the entire computer.
Accordingly, while cooling of a CPU, which is not considered as a crucial subject in the past, comes recently in the limelight as an important task which cannot be passed over, a CPU cooling fan which is used at the present stage, reveals a technical limitation by which it cannot perform a sufficient cooling function.
On the other hand, when performing a cooling function by using a micro fan, a method for increasing volume flow rate of the fan can be implemented. Volume flow rate of a fan is determined by various factors such as blade size, blade configuration, running rpm, etc., and specifically, because it is used in a fixed space, problems which can result from spatial limitations, electric power consumption and noise generation must be essentially dealt with.
Accordingly, a micro fan must be designed such that energy loss due to separation of flowing air is prevented, noise is reduced, flow loss between an inlet and an outlet of a blade is minimized and a static pressure rise is maximized, whereby a high performance of the micro fan can be accomplished.
Specifically, it was found through various experiments that most fan noise is caused by variables including rpm, gap between a blade tip and a duct, the number of blades, chord length, camber, the sweep of a blade, etc.
FIG. 1 is a front view illustrating a structure of a conventional micro fan which is generally used in these days. The drawing reference numeral 1 denotes a hub which is fastened to a shaft and is integrally rotated therewith, the drawing reference numeral 2 represents a plurality of blades which are integrally formed on a circumferential outer surface of the hub 1, and the drawing reference numeral 3 depicts a duct which surrounds the hub 1 and the plurality of blades 2 from the outside and guides air flow through a gap defined between the blade and the duct.
The hub 1 is a rotating member of a motor of the micro fan. A magnet is attached inside the hub 1, and if electric power is supplied to the hub 1, by an interaction between a stator coil being a fixed member and the magnet, the hub 1 is rotated.
The plurality of blades 2 function to supply outside air to a micro-processor while being integrally formed on the circumferential outer surface of the hub 1 and being integrally rotated therewith.
The duct 3 is placed radially outward of the blades 2, surrounds the blades 2, and performs a function of a guider which guides air sucked by the blades 2 into the micro-processor.
FIG. 2 is an enlarged partial plan view illustrating a blade configuration of the micro fan of FIG. 1. The blade 2 of the conventional micro fan has a configuration of a circular arc having a cross-section which is curved upward, and possesses one end which is coupled to the hub 1 and the other end which is inclined downward.
On the other hand, the duct 3 which is separated by a fine gap from an outer circumference of the blade 2 and surrounds the plurality of blades 2, has a lower part which is integrally connected with the fixed member of the motor and is locked to the micro-processor by a separate fastening means such as a screw.
Specifically, as seen in FIG. 1 a fine guide gap 3a which is defined between the outer circumferences of the blades 2 and an inner circumference of the duct 3 performs a function of a guider which guides smoothly outside air sucked by the blade 2 into the micro-processor.
Accordingly, if the hub 1 begins to rotate as electric power is supplied to the motor, the plurality of blades 2 which are integrally formed with the hub 1 are rotated, and outside air is sucked into the micro fan by pressure differentials between surfaces of the blades 2, to be supplied to the micro-processor.
The air flow is effected by the fact that, by a surface contour of the blade 2 which is curved upward, pressure is abruptly reduced inside rather than outside the surface of the blade 2 when the blade 2 is integrally rotated with the hub 1 and according to this, air flows from a point of high pressure toward a point of low pressure.
However, because most micro fans which are used in these days are manufactured only for the purpose of sucking air from the outside, a configuration of the blade 2 is designed in a simple way. Namely, while volume flow rate of the fan is determined by blade size, blade configuration, running rpm, etc., the cross-section of the blade 2 which is applied to the conventional micro fan has a simple configuration as shown in FIG. 2 in which both ends of a lower surface being a straight line are connected with each other by a circular arc having a predetermined radius, a blade angle which is an inclination angle of the blade 2 with respect to the hub is the same at a root and a tip of the blade 2, a camber ratio which is a ratio of a maximum height difference between the lower surface and a thickness center line to a length of the lower surface is about 10% which is a somewhat large value, and a chord line length is the same at the root and the tip of the blade 2.
If the plurality of blades 2 which are integrally coupled to the hub 1 are driven, when observing at various rpms, that is, at 8500 rpm, 9500 rpm and 10500 rpm, variations in wind pressure of the blades depending upon variations in volume flow rate which is generated by the micro fan, performance characteristics which are given in TABLE 1 are obtained.
TABLE 1 Wind Pressure (mmAq) Wind Pressure (mmAq) Volume Flow Rate 8500 9500 10500 Volume Flow Rate 8500 9500 10500 (cmm) rpm rpm rpm (cmm) rpm rpm rpm 0 1.4306 1.6943 2.2725 0.017 0.3564 0.4684 0.655 0.001 1.3435 1.6129 2.1748 0.018 0.3357 0.4476 0.6426 0.002 1.2357 1.497 2.0445 0.019 0.3191 0.4228 0.6343 0.003 1.1444 1.385 1.9223 0.02 0.2734 0.4103 0.6135 0.004 1.0449 1.2813 1.8042 0.021 0.2361 0.3688 0.5845 0.005 0.9495 1.1818 1.6984 0.022 0.178 0.3315 0.5638 0.006 0.85 1.0822 1.5592 0.023 0.1241 0.2776 0.5264 0.007 0.7712 0.9785 1.4472 0.024 0.0661 0.2237 0.4974 0.008 0.6675 0.8831 1.3186 0.025 0 0.178 0.4476 0.009 0.5804 0.7919 1.2067 0.026 0.1075 0.3896 0.01 0.5057 0.7048 1.0864 0.027 0.0536 0.3232 0.011 0.4435 0.6094 0.991 0.028 0 0.2651 0.012 0.4145 0.5555 0.8707 0.029 0.1863 0.013 0.4103 0.5223 0.7919 0.03 0.1158 0.014 0.4062 0.5099 0.7421 0.031 0.0412 0.015 0.3979 0.4933 0.6882 0.032 0 0.016 0.3813 0.485 0.6758 0.033
On the other hand, FIG. 3 is a graph which is made using performance characteristics as given in TABLE 1.
From the performance characteristic variations given and illustrated in the TABLE 1 and the FIG. 3, respectively, it is to be readily understood that the more volume flow rate is decreased, the more wind pressure of the micro fan is increased, and the more volume flow rate is increased, the more wind pressure of the micro fan is decreased.
Also, it is to be readily understood that these wind pressure characteristic variations are effected also depending upon rpm of the blade.
On the other hand, as can be seen from TABLE 1 and FIG. 3, when wind pressure is decreased by the increase in volume flow rate, a surging phenomenon in which air flow is unstabilized occurs at a point where wind pressure reduction slope is changed from an abrupt one to a gradual one. By this, there is caused a problem in that fan driving efficiency is deteriorated.
This is because a stall which retards a performance characteristic occurs when wind pressure is abruptly varied. If a hub ratio is increased, air supplying performance characteristics reveal a tendency that highest pressure is increased, a slope of a driving region is steepened and a depth of the stall is deepened.
Accordingly, due to the fact that desired cooling efficiency cannot be achieved by the conventional micro fan, overheating of a device is caused, and in order to cope with this problem, a motor having larger load capacity must be used for increasing rotating force of the micro fan.
Further, since vortex flow is structurally generated at the tip which is the outer circumference of the blade, separation of air flow is brought about, and a peripheral flow field is disturbed by the separation of air flow, whereby performance of the micro fan is impaired and noise is increased.
On the other hand, because a micro-processor of a high capacity and a high speed which have been recently developed must provide a more shortened processing time, a proper cooling cannot be implemented by the conventional blade configuration. Due to this aspect, the development of a fan blade which can satisfy the above condition has drawn considerable attention with increasing demand.